Permeability tuning



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United States Patent "ice 3,214,716 PERMEABILITY TUNING Fred F. Ruland, 22 Bradford Road, Weston, Mass. Continuation of application Ser. No. 673,286, July 22, 1957. This application Jan. 10, 1963, Ser. No. 251,467 12 Claims. (Cl. 336-131) This application is a continuation of US. application Serial No. 673,286, filed July 22, 1957, now abandoned.

The present invention relates to electrical components and electrical systems associated therewith and, more particularly, to variable inductors and electronic systems associated therewith.

The primary object of the present invention is to provide electronic components and systems with a variable inductor that possesses an unprecedented combination of desirable manufacturing and operating features by virtue of novel interrelationships among an inductive coil, a magnetic core guided for sliding movement therewithin, serrations contiguously associated with the core, and a gear in mesh with the serrations. These manufacturing and operating features include: simplified, miniaturized and self locking assembly; great mechanical and electrical stability; convenient manual or remote control; logical auxiliary tuning; adaptability for direct association with printed circuitry; and, particularly, adjustability for uniform tracking among a plurality of such variable inductors.

Other objects will in part 'be obvious and will in par appear hereinafter.

The invention accordingly comprises the device po ssessing the construction, combination of elements and arrangement of parts, which are exemplified in the following detailed disclosure, and the scope of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

- FIGURE 1 is a perspective view, partly broken away, of a miniaturized radio tuner, together with associated circuitry, comprising variable inductors constructed in accordance with the present invention;

FIG. 2 is a cross-sectional view of a sub-assembly of the tuner of FIG. 1, taken substantially along the line 22;

FIG. 3' is a side elevation of one of the components of the sub-assembly of FIG. 2;

FIG. 4 is a plan view of the component of FIG. 3;

FIG. 5 is a side elevation of another of the components of the sub-assembly of FIG. 2;

FIG. 6 is a plan view of the component of FIG. 5;

FIG. 7 is a side elevation of another of the components of the sub-assembly of FIG. 2;

FIG. 8 is a plan view of the component of FIG. 7;

FIG. 9 is a graph illustrating relationships among components of the tuner of FIG. 1; and

FIGS. 10 through 30 are views of alternate components by which the corresponding components of the device of FIG. 1 are replaceable.

Although the present invention is applicable generally to permeability tuning devices including only a single variable inductor or three or more variable inductors, by way of illustration the present invention is described herein primarily in reference to a device including a pair of variable inductors.

Generally, the illustrated embodiment of the present invention is a tuning module 24 constituting part of a superheterodyne radio receiver comprising a printed circuit panel, shown in part mechanically at 20 and in part electrically at 22.

3,214,716 Patented Oct. 26, 1965 The components of module 24 are carried by a frame 26 in the form of an open back housing composed of an electrically conducting material such as brass. Frame 26, which is generally rectangular in shape so that it may be readily chuted for automated assembly with the printed circuit panel, includes a front wall or panel 28, a pair of side walls or panels 30 and 32 and a top wall or panel 34, all formed from an integral blank. The components of module 24 include a variable inductor 36 and an adjustable tank capacitor 38 as t-uned reactances of an input radio frequency stage, and a variable inductor 40 and an adjustable tank capacitor 42 as tuned reactances of a local oscillator stage.

As shown inductor 36 includes an insulating, stiff paper sleeve 43 opened medially at 44 and terminally at 46 and 48. Wound about the portion of sleeve 43 between medial opening 44 and terminal opening 46 is an antenna coil 50, for example, of Litz wire. Slidable within sleeve 43 is a magnetic core 52, composed for example of comminuted iron particles compounded with a plastic binder, having at each of its opposite ends a slot 54 designed for engagement with a screwdriver or other alignment tool and helical threading 56 for a reason to become later apparent. Similarly, variable inductor 40 includes a sleeve 58 opened medially at 60 and terminally at 62 and 64. Wound about sleeve 58 between medial opening 60 and terminal opening 64 are an inner oscillator coil 66, for example, composed of relatively fine Litz wire and an outer tickler coil 68, for example, composed of relatively coarse lacquered copper wire. Slidable within sleeve 58 is a core 69 similarly operative to core 52 as described above, but within an inductance designed for the specific electrical requirements of the oscillator tank circuit to be described below. As shown, the extremities of sleeves 43 and 58 are encircled by plastic rings 70 having peripheral channels 72. Each of side panels 30 and 32 of frame 26 is provided with a pair of slots 74 and 76 that converge toward the free edge with which they communL cate. Channels 72 are designed to receive the inner edges of slots 74 and 76 onto which they are freely assembled and are retained in a manner to become apparent later.

Meshing with the threading on both slugs 52 and 69 through medial openings 44 and 60 of sleeves 43 and 58 is a deformable, resilient gear 77 composed of a rubberlike material, for example, a synthetic polymer such as polyethylene or a natural polymer such as rubber. Details of gear 77 and its mounting assembly are shown in FIGS. 2 through 8. Gear 77 includes an externally geared annular portion 78 and a shank portion 80 having a closed conical extremity. Shank portion 80 is pressfitted into a hollow 82 in the supporting head 84 of a shaft 86. Shaft 86 is composed of a plastic material, such as nylon, which electrically isolates the circuitry from the hand of an operator. Head 84, which fits snugly through an opening in front panel 28 of frame 26 is restrained against longitudinal movement by an integral flange 88 abutting against the inner face of front panel 28. Washer 90, which is composed of spring metal, has a rearward generally conical portion 91 and a forward generally conical portion 93. Rearward portion 91, which is more convergent than forward portion 93, being initially flattened against front panel 28 during assembly, thereafter exerts a predetermined force against head 84 of shaft 86, which is gripped by a toothed medial opening 92 in forward portion 93. A manually engageable control knob and pointer 94 is carried at the extremity of shaft 86. Rotation of shaft 86 is limited by a pair of stops 96 and 98 integral with flange 88 that are adapted to abut against a lug 100 (FIG. 1) struck inwardly from front panel 28.

Condensers 38 and 42 are mounted on the under side on an insulating plate 102. Insulating plate 102, in turn, is affixed to frame 26 by integral lugs, one of which is shown at 104, projecting through corresponding slots, one of which is shown at 106, at the lower edges of the front and side panels of frame 26. In conventional fashion, each of condensers 38 and 42 comprises a plurality of bowed conducting metallic strata, separated by interposed non-conducting dielectric strata and affixed to plate 102 by a screw 110 which extends through the conducting and non-conducting strata into a threaded opening in plate 102. Rotation of screw 110 adjusts the shape of the conducting strata and their consequent summation capacitance.

Module 24 is mechanically and electrically coupled to printed circuit 20, 22 as follows: Depending from side panels and 32 and front panel 28 are a plurality of lugs 112, which are designed for insertion into a plurality of associated slots 114 in panel 20 in order to retain frame 26 rigidly thereupon. Also depending from the lower face of insulating plate 102 are: a pair of pins 116 and 118, which are formed from integral extensions of certain metallic strata of condensers 38 and 42, respectively; a central pin 120, which is formed from other metallic strata of both condensers 38 and 42; and an independent pair of pins 122 and 124. In the illustrated embodiment, when frame 26 is so fixed upon panel 20 by mechanical lugs 112, pins 122 and 124, which are connected across coil 66 by leads 126 and 128, project into sockets 130 and 132, which are connected to a local oscillator 134. Similarly, pin 120, which is connected to the ground sides of condensers 38 and 42 and of coils and 68 by leads 135 and 137 project into a socket 136, which is connected to ground. Similarly, pins 116 and 118, which are connected to the hot sides of condensers 38 and 42 and of coils 50 and 68 by leads 139 and 141 project into sockets 138 and 140, which are connected to local oscillator 134 and a detector and mixer stage 142. In conventional fashion, the outputs of stages 142 and 134 are mixed and applied to the intermediate frequency amplifier, detector, audio frequency amplifier, and speaker stages 144 of the superheterodyne radio receiver, which the elements of the printed circuit comprise.

The various components of module 24 may be readily assembled in a self-locking manner as follows. First, head 84 of shaft 86 is inserted through the opening in front panel 28 until flange 88 abuts against the inner face of the front panel. Next, lock washer 90 is forced over shaft 86 until suitable compressive forces are exerted between the lock washer and the flange to produce a desirable friction drag against rotation of shaft 86 by manually adjustable knob 94. Next, rings are received by slots 74 and 76 so that channels 72 receive the associated edges of the slots. Then, slugs 52 and 69 are inserted into sleeves 43 and 58, respectively, so as to be accessible through openings 44 and 60. Finally, shank of gear 77 is press-fitted into hollow 82 of head 84 so that the external threading of annular portion 78 meshes with the external threading of slugs 52 and 69. Alternatively, gear 77 may be assembled before slugs 52 and 69 are threaded into mesh therewith.

Gear 77 is designed so that its diameter when undeformed is somewhat greater than the distance between slugs 52 and 69 when urged by opposing forces into their remote positions in sleeves 43 and 58. Thus, when gear 77 is properly positioned with its shank projecting into hollow 82, its threaded periphery 78 exerts opposed forces that firmly predetermine the positions of slugs 52 and {69 within sleeves 43 and 58. Additionally, these forces act on sleeves 43 and 58 to urge rings 70 toward their most inward positions within slots 74 and 76 in order to retain them stably in the positions into which they ini tially were freely inserted. Reciprocally, annular portion 78 is deformed in such a way that its outermost extremities are deformed most whereby, in consequence,

4 a continuous force tends to direct shank 80 into hollow 82 of head 84.

In order that rotation of gear 77 produce like changes in the tuning of the tank circuit that includes inductor 52 and condenser 38, and the tank circuit that includes inductor 68 and condenser 42, i.e., in order to produce proper tracking, frame 26 is composed of a non-magnetic, electrically conductive material, such as brass, which shields the inductors from the body capacitance of an operator or other external stray capacitance.

It is difficult to design two variable tank circuits capable of being tuned in unison throughout diiferent frequency ranges, for example as when one is in the input stage of a superheterodyne receiver and the other is in the oscillator stage. The tank circuit of the input stage must cover a wider frequency range and is. subject to greater circuit loading than the tank circuit of the oscillator section. It is desirable, therefore, to enhance certain electrical characteristics of the tuned input circuit in order to match corresponding electrical characteristics of the oscillator tank circuit. For this purpose, a sleeve 146, composed of a magnetic material, is provided about inductor 52, for a purpose to be described below.

In FIG. 9, the resonant frequency of an inductor of the type shown at 52 in FIG. 1, is plotted against the angular position of a shaft that moves the core via a gear of the type shown at 77 in FIG. 1, the resonant frequency being in terms of kilocycles and the angular position of range, therefore, is impractical to obtain.

the shaft being in terms of unitsof which 0 units represents a position of the shaft when the core is fully within the coil and 100 units represents a position of the shaft when the core is fully withdrawn from the coil. Curve 148 is a typical S-curve, the drop at its low frequency end being caused by the fact that the electromagnetic field extends somewhat beyond the ends of the coil so as to encompass the core completely before the core is fully within the coil. Consequently the final increments of mechanical movement result in a disproportionately small inductive change, and hence a small frequency change. The rise at the high frequency end of curve 148 is caused by the abrupt change in inductance when the core leaves the immediate field of the coil, which then becomes an air field inductor. Although a curve of this nature presents many disadvantages, it is common- 1y tolerated because of the need for tuned circuits covering frequency ratios of three to one or greater, in a reasonably compact construction. Furthermore, space considerations demand at times that electrical shielding or grounding of the type illustrated by frame 26 in FIG. 1 be placed in close proximity with the inductor. Such shielding or grounding tends to result in further distortion of the tuning characteristics as shown by curve 150.

It would be possible to utilize only the central linear portions of curves 148 and 150. However, this would result in an extremely narrow tuning range. Alternatively, it would be possible to increase the tuning range by such an amount that deletion of the non-linear extremities of the curve still would nevertheless permit a tuning ratio of three to one or greater. However, design considerations are such that tuning ratio is primarily a function of length of coil and distance of core motion. This means that for a given increase in coil length, the over-all length of the tuning unit would be increased by twice that amount when the core is Withdrawn. A large increase in tuning Further, the coil structure of such increased length may be in such close proximity to surrounding metallic objects or shielding as to give rise to a curve shape similar to that shown at 150.

In accordance with the present invention it has been found that placing magnetic sleeve 146 about the coil provides a variety of desirable effects now to be described. The first effect is to isolate the coil from the proximity effect of shielding and other metal objects. Heretofore such sleeves have been longer than their associatedcoils and have acted to provide direct paths for the magnetic flux, thereby reducing eddy current losses in associated shielding. In any event, they are proportioned to be spaced from the periphery of the coil as much as possible for the purpose of minimizing eddy currents in the magneticsleeve itself. The sleeve illustrated herein, however,-

is in close proximity to the periphery of the coil and is substantially the same length or shorter than the coil. It therefore acts in a more or less conventional manner as a shield against the losses and distortion of tuning characteristics caused by metal surroundings. It, however, coacts with the core in an entirely different manner as the core approaches its innermost position within the coil, serving partially to complete the longitudinal magnetic paths within the core, around the ends of the coil and longitudinally along the sleeve. As is well known, a given percentage of decrease in the gap distance of an inductive path causes a percentage inductive increase four times as great. Hence sleeve 146 serves as an excellent correction for the drop in the low frequency end of curves 148 and 150 as illustrated in curve 152. In reference to the high frequency end of the curve, when the core is withdrawn, the coil no longer becomes an air field inductor because of the presence of the sleeve.

In the construction of the variable inductor of the oscillator tank circuit, the tickler coil is conventionally wound, then coveredwith an overwinding of several layers of insulating paper for the purpose of increasing the diameter of the form over which the oscillator coil is then wound. The result of this construction is to alter the magnetic field surrounding the oscillator coil so that movement of the core has a lesser effect on overall inductance and attendant tuning range. In consequence, the curve of angular position of gear 77 vs. frequency response for the local oscillator tank circuit is similar to curve 152, which, with shield 146 present, represents the curve of angular position of gear 77 to frequency response for the radio frequency tank circuit. Accordingly, since both curves are of substantially the same shape, they may be superposed in operation by sequentially adjusting screws 110 of capacitors 38 and 42 and cores 52 and 69, at various rotational positions of gear 77. Rotation of the cores generally varies the vertical distance between the curves; adjustment of the condensers generally varies the horizontal distance between the curves; and changes in the inductance-capacitance ratio in each tuned circuit vary the slope of its curve.

By virtue of the resilience of gear 77, the mesh between gear 77 and slugs 52 and 69 is virtually without backlash. In order to prevent any undesired vibratory rotation of the slugs, in the illustrated embodiment, the overall cross-sectional profile of each of the slugs is circular but the pitch line of its threading is frusto-triangularly rather than circularly shaped so that the cylindrical outer diameter of the slug bears against the sleeve and-the irregular depth of thread cooperates in detent fashion with gear 77. In consequence no inadvertent rotation of the cores is possible. Such a frusto-triangular shape, for example, may be produced by intentional asymetrical centerless grinding.

Alternative construct-ions of the positive adjusting means and the resilient biasing means, shown in part in FIG. 1 as rubberlike gear 77, threaded core 52, sleeve 73 and rings 70, are shown in FIGS. through 16. In FIG. 10 an externally threaded rigid core 154 is guided for sliding movement within a sleeve 156, the opposed extremities of which are mounted within slots 158 of a frame 160 by a pair of rubberlike rings 162, similar in all respects to rings 70 of FIG. 1 except in the material of which they are composed. A gear 164, which is composed, for example, of a rigid plastic, meshes with the threading of core 154 to urge core 154 against the inner periphery of sleeve 156, the core thereby being biased against the gear by the resilience of rings 162. FIG. 11 illustrates an alternative gear and core, the core including a rod composed of a magnetic material of the typedescribed above, 166 press-fitted into an externally threaded rigid plastic tube 168 and the gear including an inner rigid portion 170 coated with a rubber or rubberlike material 172. Such a core construction is not only economical to manufacture, but is of great utility in inductor designs in which one or more circuits cover only limited tuning ranges. FIG. 12 illustrates an alternative gear and core, the core including a rigid externally threaded inner portion 174, the troughs of which are coated with a rubber or rubberlike material 176, and the gear being composed or a rigid material 178. FIGS. 13 and 14 show a spring biasing arrangement in which a gear 180, having a peripheral channel 182, is biased into mesh with an externally threaded core 184 by the medial portion of a leaf spring 186, the opposed extremities of which are secured by a pair of lugs 188. Lugs 188 are struck from the front of the frame, which is provided with an elongated slot 189 that receives the shaft on which the gear is mounted. Whereas the foregoing variations, for the most part, are applicable to single or multiple variable inductor constructions, this embodiment is applicable only to a single variable inductor construction. FIGS. 15 and 16 show a spring biasing arrangement in which a gear 181, having a peripheral channel 183, meshes with a pair of externally threaded cores and 187, while biasing them against their respective guides by means of a resilient metallic or rubberlike O-ring 189 within groove 183. In any of the foregoing embodiments involving a resilient gear, instead of rotating the core in order to effect an adjustment, it is possible to restrain the core from normal motion while rotating the gear, which is capable of resiliently being cammed into mesh with succeeding teeth of the core.

FIG. 17 shows an alternate construction in which the sleeve is replaced by a rod 190, hexagonal in cross section, that extends between the side faces 192 and 194 of a frame 196. Extending inwardly from face 192 is a tube 198 carrying a winding 200. An externally threaded rigid core 202 has a longitudinal opening, hexagonal in cross section that freely receives rod 190 and that is reciprocable within tube 198. Core 202 is resiliently biased against rod 190 by .a rubberlike gear 204 with which it meshes. Side faces 192 and 194 are provided with openings 206, the upper peripheries of which are flat as at 208. It will be apparent that a predetermined one of the flat faces of rod 190 Will tend to abut against fiat portions 208 of openings 206 in response to the bias applied by gear 204 through core 202 to rod 190.

Alternative indexing means for preventing inadvertent relative rotation between the core and the sleeve are illustrated in FIGS. 18 through 27. In FIGS. 18 and 19,

core 210 is provided with longitudinal ribs 212 that tend to find a stable position with respect to a resilient gear 214 With which the core meshes. In FIGS. 20 and 21, a core 216 is provided with longitudinal grooves 218 into which a longitudinal rib 220 of a sleeve 222 snaps in detent fashion under the bias of a resilient gear 224. In FIGS. 22 and 23, core 226 has a smooth cylindrical periphery 228 and a serrated rack 230 that tends to remain centered on a resilient gear 232, which biases it against sleeve 234. In cross section periphery 228 constitutesmore than a semi-circle and rack 230 constitutes a minor cord. Core 228 may be adjusted with respect to gear 232 by rotation until rack 230 disengages gear 232 and thereafter by longitudinal movement unaccom panied by rotation of gear 232.

FIGS. 24 and 25 illustrate alternative means for eliminating backlash between cores and gears of the foregoing type, in each case the core being illustrated as rigid and the gear as resilient. In FIG. 24, core 236 is shown as being provided peripherally with helical threading that meshes with straight teeth on resilient gear 238, whereby local distortion of the normally straight teeth of resilient gear 238 reduces backlash. In FIG. 25, core 240 is provided with threading of relatively coarse pitch and resilient gear 242 with threading of relatively fine pitch, whereby localized distortion of the resilient gear is induced in order to decrease backlash. In each of the foregoing cases, it becomes possible to decrease the size of the gear and therefore the compactness of the assembly while maintaining the same stroke of the core inasmuch as a smaller gear with a given number of teeth will move the core the same distance as a larger gear with the same number of teeth. The principles of FIG. also make it possible for a single resilient gear to mesh with threading of different pitch on a pair of cores each of which will be characterized by a difierent length of stroke in response to a given rotation of the gear in order to provide tracking in dissimilar circuitries. In FIGS. 26 and 27, core 244 is provided with threading, in the troughs of which are distributed rows of lugs 246, preferably rubberlike. Pairs of lugs 246 prevent inadvertent rotation of the core while in mesh with gear 248-.

In FIG. 28, sleeve 250 winding 252 and resilient gear 254 are identical to their counterparts in FIG. 1. Ex ternal threading 256, however, as shown, is provided at the end of a ferrite antenna rod 258 which extends through the frame on which sleeve 250 is mounted. Rod 258 thus is designed for axial movement in response to rotation of gear 254 and for Vernier adjustment by rotation with the aid of screwdriver slit 260.

In FIG. 29, an alternative structure, including a pair of ganged variable inductors is shown as including a pair of externally serrated rack-like cores 262, 264 biased against sleeves (not shown) by a pair of rubberlike gears 266, 268. Gear 268 is keyed to a shaft 270. The shank of gear 266 is press-fitted into a bore at the end of shaft 270, with respect to which it is frictionally movable by screw driver slot 272 for gross adjustment between cores 262 and 264.

In FIG. 30, core 274 is provided with a flat 276 and racks 278 and 280 at varying distances from center 282 for the purpose of permitting entry and adjustment of the pressure applied by the gear 284, as well as initial assembly, disengagement and re-engagement at different positions on the gear periphery.

Since certain changes may be made in the above device without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing be interpreted in an illustrative and not in a limiting sense.

I claim:

1. A variable inductor comprising a frame having a front and a pair of opposed sides, a gear rotatably mounted on said front between said opposed sides, said opposed sides providing a pair of slots, the axes of which are oblique with respect to the axis of said gear, a sleeve, the opposite ends of which are received by said slots, an inductive coil wound about said sleeve, a magnetic core guided by contact of its periphery with said sleeve longitudinally substantially throughout its length for sliding movement within said sleeve, a threaded conformation in contiguity with said core, said gear being in forced mesh with said threaded conformation to thereby bias said core against the inner surface of said sleeve and to bias said sleeve into said slots.

2. The variable inductor of claim 1 wherein said gear is formed of resilient material.

3. The variable inductor of claim 1 wherein said sleeve is formed with an opening therein and said gear meshes with said threading through said opening.

4. A variable inductance device, comprising a tubular support, an inductive coil carried by a portion of said support, a generally cylindrical cor-e disposed within said support, said core being formed with threads about its outer cylindrical surface, a gear mounted for rotation about an axis normal to the axis of said core, said gear extending through said support, to mesh with the threads of said core whereby said core may be axially displaced along said support by rotation of said gear, said core being provided at an end portion thereof with tool receiving means whereby said core in cooperation with said gear may be rotated about its longitudinal axis for axial adjustment of said core.

5. A variable inductance device according to claim 4 including detent stop means between said core and said support for locking said core in a selected angular position about its longitudinal axis.

6. A variable inductance device according to claim 4 wherein said gear is formed from a deformable resilient material, said gear being mounted in pressure engagement with said core.

7. A variable inductor, comprising a pair of sleeves,

means mounting said sleeves in spaced parallel relation, an inductive coil wound about each of said sleeves, a generally cylindrical core disposed within each of said sleeves, each of said cores being circumferentially threaded, a deformable, resilient gear extending between said sleeves and in mesh with the threads of both said cores, said gear being mounted for rotation about an axis perpendicular to the axes of said cores whereby said cores may be simultaneously displaced in axially opposite directions by rotation of said gear, said gear being in pressure contact with both of said cores whereby said cores are normally biased against the walls of their respective sleeves.

8. A variable inductor according to claim 7 including means for rotating at least one of said cores about its longitudinal axis for axially displacing said core independently of the other of said cores.

9. A variable inductance device, comprising an openended sleeve, means mounting said sleeve in fixed position, coil windings carried on one end of said sleeve, a generally cylindrical core disposed within said sleeve, said core being formed with threads about its outer cylindrical surface, the walls of said sleeve being formed with an opening through a mid-portion thereof, a resilient gear extending through said opening and in mesh with the threads of said core, said gear being mounted for rotation about a fixed axis perpendicular to the axis of said core whereby rotation of said gear will displace said core in an axial direction, said gear being in pressure engagement with said core whereby said core is normally biased against an inner wall of said sleeve, said core being provided at least at one end thereof with tool cooperating means whereby said core may be rotated about its longituidnal axis for axial displacement independently of rotation of said gear.

10. A variable inductance device comprising a plurality of inductance coils fixed in spaced parallel relation to one another, an externally threaded generally cylindrical core disposed coaxially with respect to each of said coils, a pinion gear mounted for rotation about an axis perpendicular to the axes of said cores and in mesh with the threads of said cores whereby said cores may be simultaneously displaced along their respective axes by rotation of said gear, at least one of said cores being provided at an end portion thereof with tool receiving means whereby said one core in cooperation with said gear may be rotated about its longitudinal axis for axial adjustment of said one core.

11. A variable inductance device according to claim 10 wherein said gear is formed from a deformable resilient material.

12. A variable inductance device, comprising a tubular support, an inductive coil carried by a portion of said support, a generally cylindrical core disposed within said support, said core being formed with threads about its outer cylindrical surface, a cylindrical member provided with peripheral teeth mounted for rotation about a fixed axis normal to the axis of said core, said member extending through said support to mesh with the threads of said core whereby said core may be axially displaced along said support by rotation of said member, said member being thereby employed as a gear, said core being 2,321,317 6/43 Plensler 7410 X provided at an end portion thereof with tool receiving 2,338,134 1/44 Sands et a1 33667 X means whereby said core in cooperation with said mem- 2,461,397 2/49 Ross. 336136 X ber may be rotated about its longitudinal axis for axial 2,462,822 2/49 Wood 336136 X adjustment of said core, said member being thereby em- 5 2,489,595 11/49 Spoor 336--136 X played as a relatively stationary nut for said core. 2,642,559 6/53 Vish 336136 X 2,820,954 1/58 Fay 336131 References Cited by the Examiner UNITED STATES PATENTS LARAMIE E. ASKIN, Primary Examiner.

2,318,415 5/43 Patzschke et a1. 336136 10 JOHN B RN Ex min r. 

1. A VARIABLE INDUCTOR COMPRISING A FRAME HAVING A FRONT AND A PAIR OF OPPOSED SIDES, A GEAR ROTATABLY MOUNTED ON SAID FRONT BETWEEN SAID OPPOSED SIDES, SAID OPPOSED SIDES PROVIDING A PAIR OF SLOTS, THE AXES OF WHICH ARE OBLIQUE WITH RESPECT TO THE AXIS OF SAID GEAR, A SLEEVE, THE OPPOSITE ENDS OF WHICH ARE RECEIVED BY SAID SLOTS, AN INDUCTIVE COIL WOULD ABOUT SAID SLEEVE, A MAGNETIC CORE GUIDED BY CONTACT OF ITS PERIPHERY WITH SAID SLEEVE LONGITUDINALLY SUBSTANTIALLY THROUGHOUT ITS LENGTH FOR SLIDING 